Cathode-ray tube projector



Feb. 4, 1947. c. s. SZEGHO CATHODE R AY TUBE PROJECTOR Filed Dec. 23,1944 w J mi F m & 7 M $0 Y M ATTORNEY Patented Feb. 4, 1947 'lf'A'lESPATENT OFFICE GATHODlE-RAY TUBE PROJECTOR Constantin S. Szcgho, Chicago,111., assignor to The Rauland Corporation, Chicago, Ill., a corporationof Illinois 3 Claims.

This invention relates to new and useful improvements in cathode raytube projectors of the kind employed in large screen televisionreceivers. This is a division of my application Serial No. 442,835,filed May 13, 1942.

The object of the invention is to increase the light output ofprojectors using a mirror optic, such as the Schmidt camera. (James G.Baker: The solid-glass Schmidt camera and a family of flat-fieldcameras, equivalent in performance to the Schmidt camera. Proceedings ofAmerican Philosophical Society, vol. 82, No. 3, April 30, 1940.)

In the Schmidt camera type of projector a cathode ray tube havingfluorescent material deposited on a transparent support, usually a wallof the cathode ray tube, is located between a large diameter sphericalmirror and a correcting plate. The light is first produced at thecathode or back side of the surface of the fluorescent powder and thenpasses through the powder to emerge from the front surface contactingwith the transparent support, usually the end Wall of the tube. Theelectrons impinge on the back side surface of the layer. The outsidesurface faces the spherical mirror. In such back surface projection muchof the light is lost by absorption in the fluorescent layer.

In accordance with the present invention, the light output of theprojector is increased by providing a front surface projection cathoderay tube between the mirror and the correcting plate of a Schmidt cameratype of optical system.

In the drawing:

Fig. 1 is a diagrammatic illustration of one embodiment of thisinvention; and

Figs. 2 and 3 illustrate two methods for assembling the tube of Fig. 1.

An embodiment is illustrated in Fig. 1 in which 2! is an evacuated glassenvelope having a neck 22. The neck encloses an electron gun 23 andvertical and horizontal deflecting plates 2 The bell-shaped main chamberof the envelope 21 contains a disc 25 of aluminum having a thickness ofapproximately 5 microns. The disc is curved and has its convex surfacecoated with a layer of fluorescent material 26. The curved end wall 21of the envelope 2! is parallel with the adjacent coated aluminum disc 25and faces a spherical mirror 28. The neck 22 of the tube projectsthrough a central opening in a correcting plate 28. The mirror 28 andplate 29 constitute a Schmidt camera type of optic, the radius ofcurvature of the disc 25 being the focal length of the optic.

High voltage electrons produced by the gun 23 will pierce the aluminummember 25 and penetrate the fluorescent layer 26 to cause the eXcitationof its outside surface near the window 21 which will allow substantiallyall the light from the fluorescent screen to reach the mirror 28. At thecustomary anode voltage of approximately 50,000 volts, the energy lossof electrons going through such aluminum disc is only about 5%. Nonegative charge will be present to slow down the electrons which can,therefore, penetrate to a suflicient depth into the fluorescent layer 26to produce the necessary light effects.

If the space between the spherical mirror and the correcting plate isfilled with a liquid of high refraction index the light output of thisarrangement can be further increased by a factor which is the square ofthe refraction index. Instead of filling the space with an immersionliquid this space can be filled with solid material such as glass orplastic. In this case the spherical mirror and the correcting surfacewill preferably constitute the end faces of the solid.

Figs. 2 and 3 show two arrangements for assembling the tube structureschematically illustrated in Fig. 1. In Fig. 2, the curved aluminum disc25 is mounted on wires 30 connected with the anode structure 3! in theneck 32 of a glass envelope. The body of the envelope 33 is cylindrical,the end of which may be closed by a flat glass window 34 during whichoperation the anode structure with the fluorescent screen is withdrawntowards the cathode. In the structure shown in Fig. 3, the aluminum disc25 is supported 0n wires 35 which are sealed into the wall of cylinder36, one end of which is closed off by a flat window 31; the other openend may be joined to the neck portion 38 of the tube at such a distancefrom the aluminum member that it wil1 not be damaged. What I claim is:

1. In combination, a fluorescent layer, a layer of conducting materialin contact therewith, an electron gun emitting electrons which penetratethrough said conducting layer into said fluorescent layer, a mirror forreflecting 1ight emanating and emerging from the exposed surface of saidfluorescent layer, and a correcting plate in the path of the light raysreflected by said mirror.

2. In combination, a fluorescent layer, a layer of conducting materialtherefor, an electron gun emitting electrons which penetrate throughsaid conducting layer into said fluorescent layer, an evacuated envelopehaving a transparent end wall parallel with said conducting layer andthrough 3 which said fluorescent layer is visible and a neck enclosingsaid gun, a mirror for reflecting light emanating and emerging from theexposed surface of said fluorescent layer, and a correcting plate in thepath of the light rays reflected by said mirror.

3. In combination, a fluorescent layer, a convex layer of conductingmaterial therefor, an electron gun emitting electrons which penetratethrough said conducting layer into said fluorescent layer, an evacuatedenvelope having a transparent end made parallel with said conductinglayer and adjacent thereto and a neck opposite said conducting layer andsymmetrically positioned with re spect thereto, said neck enclosing saidgun, a Spherical mirror for reflecting light emanating and emerging fromthe exposed surface of said fluorescent layer, and a correcting plate inthe path of the light rays reflected by said mirror, and having acentral aperture through which said neck pro- J'ects.

CONSTANTIN S. SZEGHO.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,336,134 Szegho Dec. 7, 19432,298,808 Ramberg Oct. 13, 1942 2,295,779 Epstein Sept. 15, 1942

